This invention relates generally to the transport of webs and, more particularly to the guidance of a freshly coated web through a change in the direction of its advance.
It is known in the art that webs can be turned around a so-called air bar. For example, in U.S. Pat. No. 4,059,241 to DeRoeck et al., an advancing film separates inner and outer zones, the outer zone being under atmospheric pressure, while the inner zone is provided with compressed air. A dividing gap through which air flows from inside to outside is formed automatically due to the pressure difference, so that a contact-sensitive surface on the inner side of the film does not come into contact with a guide surface. In order to seal the inner zone from the atmosphere, sealing plates are provided that extend across the entire width of the film and can come into contact with the contact-sensitive surface. In order to prevent this happening as far as possible, air exit slits are provided in the sealing plates. The flow of air issuing from these slits, however, can likewise impair the contact-sensitive surface of the web.
In U.S. Pat. No. 3,638,845, Herzhoff et al. disclosed an apparatus in which a web is lifted by excess pressure in an inner zone sufficiently far from a cylindrical guide roll for air exit openings arranged on a circular path in both side walls to be partially unblocked by the web. A sealing strip extending across the entire width of the web is arranged between the beginning and end of the guide region. The web is respectively guided between a sealing roll that extends across the width of the web at the outer side of the web and the sealing strip. Here, too, there is a danger that the contact-sensitive surface of the web may come into contact with the sealing strip.